When remote-control valves in construction machines of this type are quickly operated, pilot pressures output from pressure-reducing valves of the remote-control valves suddenly changes and a surge in pressure occurs in pilot lines. This causes quick operation or control valves and generates shock.
To solve this problem, a technology described in Patent Document 1 is well known.
This will be illustrated in FIG. 18 that is newly drawn for comparison.
Reference numbers 1, 2, and 3 denote a hydraulic actuator (a hydraulic motor as an example thereof), a hydraulic pump serving as a hydraulic sources and a control valve of the hydraulic pilot type that controls the operation of the hydraulic actuator 1 respectively. Pilot lines 4 and 5 are connected to pilot ports 3a and 3b, respectively, at either end of the control valve 3.
A remote-control valve 6 operates the control valve 3, and downstream-pressure (secondary-pressure) lines 7a and 8a of a pair of pressure-reducing valves 7 and 8, respectively, of the remote-control valve 6 are connected to the pilot lines 4 and 5, respectively. The downstream pressures of the pressure-reducing valves 7 and 8 according to operation amounts to a lever 9 are supplied to the control valve 3 via the pilot lines 4 and 5, respectively. Reference number 10 denotes a pilot pump serving as a hydraulic source for the remote-control valve 6 (both the pressure-reducing valves 7 and 8).
In this technology (hereinafter referred to as a known technology), first throttles 11 and 12 are disposed on the pilot lines 4 and 5, respectively. Moreover, bleed-off lines 13 and 14 are branched from the pilot lines 4 and 5 downstream of the first throttles 11 and 12, respectively, and communicate with tanks T. Second throttles 15 and 16 are disposed on the bleed-off lines 13 and 14, respectively.
With this structure, the absolute values of the downstream pressures (pilot pressures supplied to the control valve 3) output from the pressure-reducing valves 7 and 8 are reduced by the first throttles 11 and 12, and at the same time, rises in the pilot pressures are moderated by the second throttles 15 and 16. With this, a surge in pressure in the pilot lines 4 and 5 during quick operation is prevented, and the shock is moderated.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2001-208005